The prevalence of obesity among adults in the United States is high, approaching 60% for black women, with likely contribution of sedentary occupations. We proposed that regular nutritional counseling at the work place would facilitate weight loss in overweight and obese female employees with a large minority representation. One hundred, ninety-nine non-diabetic women were randomized to regular meetings and weigh-ins with a dietitian (intervention) or control; all were provided Web-based nutritional and lifestyle information, advised to reduce daily energy intake by 500 kcal, instructed to increase daily pedometer counts by 5000 over baseline and given access to fitness rooms at the work place. Three-day food records, body composition (DXA), lipids, glucose, insulin, and exercise performance were measured at baseline and 6 month visits. At 6 months, 139 subjects (55% of African descent) who completed the program reported decreased daily total energy and fat intake (p< 0.001), with significant reduction in weight (-35%) and fat mass (-59%); improved insulin sensitivity (+697%); reduced total cholesterol (-512%) and triglyceride (-628%) levels; and improved exercise performance (7.314.1%) (all p< 0.001). There were no significant differences between intervention and control subjects in these outcome measures. Intervention subjects in the highest tertile of attendance (&#8805; 80% of sessions) lost significantly more weight (-4.23.8 vs. -0.92.8 kg, p=0.001) and fat mass (-3.33.5 vs. -0.82.1 kg, p= 0.007) than women in the lowest tertile (<65%) of attendance. We conclude that overweight and obese female employees provided with Web-based information and worksite exercise resources significantly improve health measures. Consistent attendance at nutrition counseling and weigh-in sessions may facilitate greater weight and fat loss. Obesity is associated with increases in both fat and lean masses. Increased lower extremity muscle mass may be compensatory to fat mass load, but the relation of upper extremity lean mass to obesity is unclear. We propose that elevated insulin levels may contribute to both lower and upper extremity lean masses in overweight or obese women. The following measurements were performed in 197 non-diabetic women (57% black, 35% white; age 4611 years meanSD, BMI range 25.0 to 57.7 kg/m2): dual-energy X-ray absorptiometry for fat and extremity lean masses; exercise performance by peak oxygen consumption (VO2 peak) during graded treadmill exercise; fasting insulin and in 183 subjects insulin sensitivity index (SI) calculated from the minimal model. SI (range 0.5 to 14.1 liter/mU-1min-1) was negatively, and fasting insulin (range 1.9 to 47.6 U/mL) positively, associated with both lower and upper extremity lean masses (all P<0.001), independent of age and height. Sixty-seven percent of women completed 6 months of participation in a weight loss and exercise program: Reduction in fasting insulin (7.96.4 to 6.76.5 U/mL, P=0.001) was associated with a decrease in both lower (P=0.025) and upper (P=0.014) extremity lean masses, independent of reduction in fat mass or improvement in VO2 peak, and without significant change in SI or interaction by race. Thus, hyperinsulinemia in overweight or obese women is associated with increased lean mass in weight-bearing as well as non-weight-bearing extremities, which is partially reversible with reduction in fasting insulin concentration, consistent with stimulatory effects of insulin on skeletal muscle. Subjects at risk for atherosclerosis may have dysfunctional high-density lipoprotein (HDL) despite normal cholesterol content in plasma. We considered whether efflux of excess cellular cholesterol to HDL from obese subjects is associated with impaired arterial endothelial function, a biomarker of cardiovascular risk. Fifty-four overweight (body mass index 25 C 29.9 kg/m2) or obese women (body mass index 30 kg/m2), age 46 11 years, were enrolled in a worksite wellness program. HDL cholesterol averaged 57 17 mg/dL and was inversely associated with BMI (r= -0.419, P= 0.002). Endothelial function was assessed by brachial artery flow-mediated dilation (FMD). Cholesterol efflux from 3H-cholesterol-labeled BHK cells transfected with the ATP-binding cassette transporter 1 (ABCA1) showed 8.2 to 22.5% cholesterol efflux over 18 hours when incubated with 1% serum and was positively correlated with FMD (P <0.05), especially in the 34 obese subjects (r= 0.482, P= 0.004). This relationship was independent of age, HDL or low-density lipoprotein cholesterol concentrations in plasma, blood pressure or insulin resistance by stepwise multiple regression analysis (= 0.31, R2= 0.21, P= 0.007). Nitration of apoA-I tyrosine residues (by sandwich ELISA) was significantly higher in obese women with the lowest cholesterol efflux than in overweight women with the highest cholesterol efflux (P= 0.01). We conclude that decreased cholesterol efflux via the ABCA1 transporter is associated with increased nitration of apoA-I in HDL and is an independent predictor of impaired endothelial function in obese women. This suggests that functional measures of HDL may be better markers for cardiovascular risk than HDL cholesterol levels in this population.